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MG TD TF 1500 - update on SU jet & fuel height!

I have just needed to re center the jet on one my H4 SU carbs.
When finished I measured the jet height with the mixture nut full up. it was .160" below the bridge, Ok.
Then I went 10 flats down, as per written. documents, as recommended for the best fuel atomization of .060"-.065" it was 0550" !!
12 flats down .0635!!
So the threads per inch on the mixture adjustment is 00529. And Not .063" that have been stated on many publications
Note I have always use Joe Curto for SU rebuild kits
BTW setting the fuel height the fuel below the bridge at the lower level of recommended .1875"-.250, like .220"-.250" greatly reduces vapor lock concerns.
I feel like a Monkeys uncle!
Len
Len Fanelli

Oops! I forgot to include the .160" in the calculation in the threads per inch! This means the threads per inch = .0063" more than likely.
(Brain fade!)
Len
Len Fanelli

Good progress Len. Glad to see its working for you and you have also improved the vapor lock issues too.
Christopher Couper

Thanks Chris, now chapter #2
I learned how to better modify the SU needles from a while back.
My mistake was making the RPM low range was too rich.
I just nailed it filing a second set needles only just passed station #4 to the end of the needle
Still a not as good as I wanted... I found a set of red dashpot springs that had a wire diameter of .026" The red ones that I was using had a wire diameter of .036"!! Now much better from 1800-3000 RPM
But once the RPM hits 3000 RPM WOW up to 5500!
Oh, I am using MGA 1622 AO needles and still idles at
800-1000 RPM.
BTW I learned that the SU pistons at full throttle only goes to just past station 4!
Now I have the Street Racer TD than I could not afford when I was a kid:)!
Safety Faster
Len
Len Fanelli

Well. Let’s go rip up the backroads!!!

Bill Chasser
TD-4834
TD/c-8151




W A Chasser

BTW after cleaning and lubricating the jet tube and mixture nut, again! The jets can now be adjusted to be flush with the bridge = ,002" & .009" below the bridge. So .0063" TPI is correct.
Len
Len Fanelli

This thread was discussed between 17/07/2026 and 25/07/2026

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